1. Field
Various exemplary embodiments of the present invention relate to a ramp signal generator for generating a ramp signal (ramp voltage) and, more particularly, to a ramp signal generator having a noise canceling function, which cancels noise contained in differential ramp signals provided from a ramp signal generation block using a voltage buffer or a programmable gain amplifier (PGA), and outputs a single-ended ramp signal.
2. Description of the Related Art
In general, a ramp signal generation block using a current steering digital-analog converter (DAC) is applied to a complementary metal oxide semiconductor (CMOS) image sensor (CIS) using a column parallel single-slope analog-digital converter (ADC). The ramp signal generation block generates a ramp signal (ramp voltage) based on a power supply voltage or a ground voltage. Thus, when the single-ended ramp signal is outputted, power noise or ground noise may be contained in the outputted ramp signal. Furthermore, noise from the ramp signal generation block (simply referred to as “ramp noise”) is not filtered, but contained in the outputted ramp signal. This noise increases the overall horizontal noise in the CIS.